Arion was an immortal horse in Greek mythology, which was very fast and bred by the gods. According to a source, it also had the ability to speak. The various sources differ on how the horse was bred. Some say that it was foaled by the goddess Demeter after sleeping with Poseidon, while others that it was the goddess of Earth, Gaea, that gave birth to it. Its most notable owner was Adrastus, king of Argos. Arion is also mentioned in the myth of Heracles against the Eleans, in which the demigod took the stallion from Oncus. He then rode on Arion during the war, and gifted it to Adrastus afterwards. During the battle of the Seven Against Thebes, in which the brothers Eteocles and Polynices killed each other while vying for the Theban throne, Adrastus was the only attacker to survive thanks to Arion's intervention.